Refrigeration system with compressor unloading means



Feb. 17, 1970 D. D. KAPICH REFRIGERATION SYSTEM WITH COMPRESSORUNLOADING MEANS 3 Sheets-Sheet 1 MN moEmomdSw INVENTOR. DAVORIN D-KAPICH ATTORNEY 4 Feb. 17, 1970 D. D. KAPICH 3,495,418

REFRIGERATION SYSTEM WITH COMPRESSOR UNLOADING MEANS Filed April 18,1968 3 Sheets-Sheet 2 HARGE INLET INVENTOR. DAVORIN D. KAPICH ATTORNEYD. D. KAPICH 3,495,418

REFRIGERATION SYSTEM WITH COMPRESSOR UNLOADING MEANS Feb. 17, 1970 5Sheets-Sheet 3 Filed April 18, 1968 H @C TP A v m mD m R W A D ATTORNEYUnited States Patent f 3,495,418 REFRIGERATION SYSTEM WITH COMPRESSORUNLOADING MEANS Davorin D. Kapich, San Diego, Calif., assignor to TheGarrett Corporation, Los Angeles, 'Calif., a corporation of CaliforniaFiled Apr. 18, 1968, Ser. No. 722,412 Int. Cl. F25b J /1 F04d 27/00 US.Cl. 62-227 Claims ABSTRACT OF THE DISCLOSURE A refrigeration systemhaving a constant speed centrifugal compressor with two or more stagesarranged in series and means for unloading and reloading the stages oneat a time as the cooling requirements decrease and increaserespectively.

Centrifugal compressors have the inherent characteristic that at a fixedspeed the discharge pressure increases when the flow requirementsdecrease. Therefore, when centrifugal compressors are used forrefrigeration purposes, means are needed to lower the compressorcapacity when the load requirement is low. Decreasing the compressorcapacity keeps the output pressure within reasonable limits and alsoprevents liquid refrigerant from slugging the compressor i.e., preventsliquid from entering the inlet of the compressor. Obviously, continuousstopping and starting of, for example, a five horsepower motor operatinat high speed is not practical. In the past, the capacity of a highspeed centrifugal compressor had been decreased by bleeding some of thehot, high pressure gas discharging from the compressor into the intakeof the compressor where the gas vaporizes any liquid in the intake toinsure that the compressor is filled with a gas. However, this method isinefficient because a large portion of flow is being throttled fromdischarge to inlet.

An object of this invention is to provide a relatively low speedcentrifugal compressor operating at constant speed wherein therefrigerant is compressed in steps as it moves from one stage to thenext. Then, as the cooling requirements drop, means are provided forunloading the stages one at a time so that the intake pressure remainswithin given limits, achieving at the same time reduction in refrigerantflow delivered to the condenser.

Another object of this invention is to provide an improved relativelylow speed, centrifugal compressor that compresses gases to a relativelyhigh pressure wherein liquid slugging does not deteriorate the impellerblades.

Briefly, the invention comprises a constant speed centrifugal compressorhaving two or more stages in series of the type taught in United StatesPatent No. 3,292,899. The gas is first compressed within one stage, thencoupled to the next stage to be further compressed, etc., until the gasis at the desired condensing pressure. In a condenser, the vapor iscooled to a liquid which is evaporated in a suitable evaporator toabsorb heat. Valve means are provided between each stage to allow therefrigerant to flow unrestricted between discharge and inlet of selectedstages when required. Control means are provided to operate and controlthe valve means in response to the cooling demands of the system so thatwhen the cooling demand is at the lowest requirement only one stage isused to compress the gas and when the cooling demand is at the highestrequirement all the stages are used to compress the gas. The compressorinherently operates at relatively low speeds so that, if slugs of liquidenter the first stage, the compressor is not damaged.

These and other objects of this invention become apparent as thefollowing description is read in conjunction with the drawings in which:

FIG. 1 is a schematic diagram showing the refrigeration cycle of theinvention.

FIG. 2 is an axial cross-section of a relatively low speed compressorthat incorporates the refrigeration cycle shown in FIG. 1;

FIG. 3 is a section taken substantially on line 33 in FIG. 1 and viewedin the direction of the arrows;

FIG. 4 is a section taken substantially on line 4-4 in FIG. 1 and alsoviewed in the direction of the arrows; and

FIG. 5 is a graph of the discharge pressure versus refrigerantvolumetric flow rate based on the inlet vapor density of the compressorshown in FIG. 1.

Referring to the drawings and to FIG. 1, in particular, there is shown aschematic refrigeration system incorporating the novel refrigerationcycle. Shown schematical- 1y is a centrifugal compressor 11 having threestages, stage A, stage B and stage C. The compressor 11 is powered by asuitable constant speed motor (not shown) which rotates a shaft 12 thatis coupled to the three stages. The stages A, B and C have suitableinlets 13a, 13b and 130, and outlets 14a, 14b and 146, respectively,which are connected by suitable tubing 15 through which the refrigerantflows. Outlet is coupled to a condenser 16 wherein the refrigerant isliquefied and stored in a reservoir 17. The liquid leaves the reservoirthrough tubing 18 and expands through a conventional refrigerantexpansion valve 21. The refrigerant enters an evaporator 22 andvaporizes. The vapor or gas is ducted to compressor 11 through a tubing20.

Since shaft 12 is continuously rotated by the motor at a constant speed,this invention includes a means that is independent of the rotationalspeed for controlling the cooling capacity of the system in relation tothe cooling requirements. The means utilizes the fact that in a.standard compression-expansion refrigerant system, the pressure of therefrigerant leaving the evaporator 22 is directly related totemperature. For example, the means includes two pressure transducers 26and 27 which are coupled to the evaporator 22 through a T-branch tubing28. The function of transducer 26 is to apply a signal, for example, apositive voltage to a lead 31 whenever the pressure in the evaporator 22is below a set minimum value. The function of transducer 27 is to applya signal, for example, a positive voltage to a lead 32 whenever thepressure in the evaporator 22 is above a set maximum value. The signalsoutputted by transducers 26 and 27 are fed through suitable gates to astage A flip-flop 33 and a stage B flip-flop 34, which will be describedmore fully hereinafter. In addition, tthe means includes two solenoidvalves 36 and 37 wherein the valve 36 is connected across stage A andvalve 37 is connected across stage B through suitable tubing. Valves 36and 37 are two normally closed solenoid valves. When both valves 36 and37 are closed, all the'stages A, B and C are in series, i.e., therefrigerant is compressed to successively higher pressure in each stage.

Whenever only valve 36 is energized by a power supply 38, valve 36opens, and only stages B and C contribute etfectively to the compressionprocess. Stage A is more or less windmilling the refrigerant thoughwithout significant pressure rise. The operating point of the stage A isas shown on FIG. 5 as point B. Operating point of stages B+C combined isshifted from point F (when all three stages A+B+C were operating inseries) to a point G on the B+C operating curve. Thus, the opening ofthe valve 36 has resulted in a reduction in the net flow delivered tothe condenser from point F to point. G. The amount of flow bypassedthrough the valve 36 from stage A discharge to the stage A inlet is thenequal to the difference between the flow at point E, minus the fiow atpoint G. Since the refrigerant vapor density at the compressor inlet isnot changing appreciably, the volumetric flow represents at the sametime the weight flow rate which is directly proportional to the coolingcapacity of the system.

Whenever both valves 36 and 37 are energized, they both open and onlystage C compresses the refrigerant. Stages A and B are both windmillingthe refrigerant though without significant pressure rise. The operatingpoint of the stage C is now shown on FIG. 5 as point H, thus reducingthe net flow delivered to the condenser from point G (when B-l-C stageswere operating in series) to the flow indicated by the point H. Theamount of flow bypassed through the valve 37 is now equal to thedifference in flow indicated by a point I minus the flow indicated by apoint H. Flow bypassed through the valve 36 equals the difference inflow between points E and H. Stage A is now operating at the point E,and the stage B is operating at point I. In this embodiment valve 37 ispreferably closed while valve 36 is closed, and is open if valve 36 isopen. However, valve 36 could be open while valve 37 is closed as willbe explained hereinafter.

The refrigeration system operates as follows: Initially, lead 32 has ahigh positive voltage coupled thereto by transducer 27 and lead 31 is atground potential since the complete system is at ambient temperature andthe pressure in the evaporator is relatively high. Lead 32 couples thepositive voltage to the reset input r of the stage B fiiplop 34 to resetthe flip-flop. When the flip-flop 34 is reset, the reset output Rapplies a positive voltage to lead 41. The positive signal in lead 41 isfed through a suitable delay circuit 42 (for reasons that will becomeapparent hereinafter) and into one of the inputs of an AND gate 43. Theother input of AND gate 43 has coupled thereto the positive signal onlead 32. Since the AND gate 43 is of the type that only outputs apositive voltage when both inputs have positive voltage coupled thereto,its output lead 44 couples a positive voltage to the reset input r ofstage A flip-flop 33 to reset the flipflop so that its reset output Rcouples a positive voltage on a lead 46. Flip-flops 33 and 34 are of thetype that switch states at the leading edge of a positive voltage andremain in that state until the leading edge of a rising voltage iscoupled to the other input. When both flip-flops 33 and 34 are reset,their respective set outputs S are at ground potential thereby placingleads 47 and 48 at ground potential. Leads 47 and 48 are coupled tosuitable relay switches 51 and 52, respectively, which are in serieswith a power supply 38 and the respective valves 36 and 37. The relayswitches 51 and 52 operate so that they close the respective circuitsonly when the respective leads 47 and 48 have a positive voltage coupledthereto.

As the rate of refrigerant liquefied in the container 17 and expanded inevaporator 22 diminishes, the temperature and the pressure of therefrigerant in the evaporator 22 and tubing 20 decreases because of thecompressor tendency to extract constant amount of flow from theevaporator. When the pressure drops below the pressure set in transducer27, the positive potential is removed from lead 32, and both leads 31and 32 are at ground potential. If the temperature cannot be controlledby ex pansion valve 21, the temperature of and the pressure in theevaporator drops to the value whereby transducer 26 couples a positivevoltage to lead 31. Lead 31 is coupled to the set inputs of stage Aflip-flop 33 and also to an AND gate 54 whose output is coupled to theset inputs of flip-flop 34. The flip-flop 33 switches to the set statecausing the set output S to couple a positive voltage to the lead 47. Adelay circuit 45 prevents the positive potential on the lead 47 frombeing coupled immediately to AND gate 54. The positive voltage on lead47 causes solenoid 51 to open valve 36. Now, the net refrigerant flowdelivered by the compressor decreases from point P to point G (FIG. 5)as previously described. Since less flow is now being taken from theevaporator, the pressure in tubing 20 rises above the set pressure intransducer 26 and the potential on lead 31 drops to ground. The functionof delay circuit 45 is to prevent the positive potential on lead 31 frombeing coupled to AND gate 54 until the pressure rises in the evaporatordue to one stage being unloaded. Flip-flop 34 remains in the resetstate.

In this condition with one stage unloaded the refrigeration system couldoperate in one of three ways. First, if the refrigeration requirementsstay substantially the same, the pressure in tubing 20 remainssubstantially constant and the expansion valve 21 controls the flow ofre= frigerant. Second, if the refrigeration requirement increases, thepressure in tubing 20 rises indicating that the evaporator temperatureis rising. When the pressure rises sufficiently, transducer 27 places apositive potential on lead 32. Since the lead 41 has already had apositive potential coupled thereto, delay 42 has coupled the positivevoltage to one lead of AND gate 43 therefore gate 43 passes a positivepotential to the reset input 2 of flip-flop 33 and solenoid 51 isde-energized. Stage A is again loaded in the system and, since therefrigerant is compressed sequentially in all three stages (shown aspoint P on FIG. 5 the pressure in tubing 20 drops. Third or last, if therefrigeration requirement further decreases when valve 36 is open,transducer 26 again places a positive potential on lead 31 because thepressure in the evaporator drops. With flip-flop 33 being set for sometime, the delay 45 coupled to lead 47 has coupled the positive signal toone of the input leads of AND gate 54. On the rising leading edge of therising voltage in lead 31, stage B flip-flop 34 is switched to the setstage and the set output S couples to lead 48 a positive potential.Solenoid 52 is also energized and valve 37 is opened along with valve36. The refrigerant flow now decreases to point H (FIG. 5) for reasonspreviously described.

When the refrigeration system is in this low output condition and if therefrigeration requirement increases, the pressure in tubing 20 rises.When the pressure is equal to the pressure set in transducer 27, apositive potential is coupled to lead 32. The flip-flop 34 is resetimmediately, but, since delay 42 is placed in series with flip-flop 34and AND gate 43, flip-flop 33 is not reset. At this point, valve 37 isclosed and valve 36 is open. The delay time of delay 42 is sufiicientlylong to allow the compressor to drop the pressure in tubing 20 to causethe positive potential on lead 32 to be removed. If the coolingrequirement is still relatively large, transducer 27 will again place apositive potential on lead 32 to cause flipflop 33 also to be switchedto the reset state. At this point both valves 36 and 37 are closed andthe refrigerant is now compressed in all the three stages to providemaximum refrigeration.

Referring to FIG. 2, there is shown a compressor employing the teachingsof this invention, and also the teachings disclosed in theabove-mentioned United States Patent No. 3,292,899. The compressor 100includes the three stages A, B and C powered by the shaft 12. The shaft12 is preferably hollow for reasons that will be described hercinafterand is bearing mounted at its end by bearings 101 and 102. The left sideof the shaft 12 is coupled to a suitable electric motor. For example, acage 103 is fixed on the shaft and is surrounded by suitable magneticfield poles 104 to form a standard constant speed A.C. (alternatingcurrent) induction motor. Field poles 104 are mounted within. a housing105.

The three compressor stages A, B and C are mounted on the right side andinclude the following components, for example, the toroidal compartmentfor stage A includes a circular half member 106 having an outwardlyextending flange 107 that is suitably fixed to the housing 105. Halfmember 106 has also an inwardly extending flange 108 to support asuitable seal 175 between it and the shaft 12. The toroidal compartmentalso is made of an inner circular quarter-member 111 and an outercircular quarter-member 112 which are both suitably fixed to flanges 108and 107, respectively, forming a circular opening or torus. Within theopening extends a plurality of impeller blades 113 that protrude axiallyfrom a wheel 114 that is, in turn, keyed to shaft 12 so that the wheel114 and impeller blades 113 rotate with the shaft. Disposed within thetoroidal compartment is a ring 116 that is held in place by an outwardlyextending lug 117 more clearly shown in FIG. 4. In the region of lug 117suitable passageways are provided for the refrigerant to ingress andegress from the stage. The refrigerant enters through a port 118 formedin an appendage 119 to the housing 105. The refrigerant is guided intothe toroidal compartment by suitable baffles, for example, radialbaflles 121 and 122 (FIG. 4) that are axially disposed, the lug 117, andinclined baflle 123 (FIG. 2) that is tangentially disposed to halfmember 106.

The impeller blades 113 and wheel 114 are rotating, for example,counter-clockwise as viewed in FIG. 3. Therefore, the refrigerant flowsin a helical path that encircles the ring 116 and also the axis of thecompressor, as illustrated by a line 115 (FIG. 4) with arrowheads. Therefrigerant flows and is compressed according to the principles taughtin US. Patent No. 3,292,899. The refrigerant leaves stage A through asuitable passageway or diffuser formed on the right side of lug 117 (asviewed in FIG. 2) and enters stage B. Stage B is made similar to stage Awith a half member 126, outer flange 127, inner flange 128, innerquarter member 129, and outer quarter member 130 forming the toroidalpassageway. Stage B also includes a plurality of impeller blades 131mounted on a wheel 132 also keyed to shaft 12. A ring 133 is alsoprovided in stage B and held in place by a lug 134. Stage B propels therefrigerant in the same manner that stage A propels it to furthercompress the refrigerant. The refrigerant egresses from stage B througha suitable passageway or diffuser formed on the right side of lug 134(as viewed in FIG. 2) and enters stage C. Stage C also is made similarto stage A and includes a half member 141, outer flange 142, innerflange 143, inner quarter member 144 and outer quarter member 145forming the toroidal passageway. There is provided a plurality ofimpeller blades 147 mounted on a wheel 148 also keyed to shaft 12. Aring 149 is provided in the toroidal passageway of stage C and held inplace by a lug 151. Outer quarter member 145 is attached to an end cover152 which supports the bearing 102 for the shaft. The refrigerant isfurther compressed in stage C and then egresses through a passageway 153to the condenser 16 since the refrigerant in one stage is at a higherpressure than the refrigerant in a preceding stage, suitable seals 175,176, 177 and 178 are provided around the shaft 12 to contain therefrigerant Within the compressor 100 and within the stages. The loadingand unloading means for the stages ,of the com pressor is providedwithin appendage 119. As shown in FIGS. 3 and 4, appendage 119 has anaxially disposed passageway 136 with ports 137 and 138 (FIG. 2) disposedtransversely. Passageway 136 communicates with inlet port 118 andcommunicates with stage B through port 137. The solenoid valve 36 ofFIG. 1 is used to open and close port 137 as shown in FIG. 3. As in theschematic system shown in FIG. 1, when valve 36 opens port 137, therefrigerant flows relativel unrestricted from discharge to inlet of thestage A. The valve 37 similarly couples and uncouples discharge of thestage B with the compressor inlet 118 via passageway 136.

The compressor embodiment shown in FIGS. 2, 3 and 4 is a preferredembodiment because, as shown in FIG. 5, the pressure at the dischargeend varies at a relatively larger rate than and inversely to refrigerantflow rate. When both valves 36 and 37 are open the performance of thecompressor is illustrated by the curve marked stage C. When valve 36 isthe only valve open, the performance of the compressor is illustrated bythe curve marked stages B+C. When all valves are closed, the performanceis illustrated by the curve marked stages A+B+C. As mentioned, thecurves are relatively steep, and therefore, when the pressure becomestoo large for the rate of flow, the compressor is made to operate on theadjacent curve and still maintain a pressure head that is sufiicient toliquefy the refrigerant. If the system is only operating with stage Ccompressing the refrigerant, and the temperature of the evaporator dropsto a relatively low temperature, liquid slugging would not degrade thecompressors since the flow of refrigerant is relatively low and thespeed of the impeller blades is relatively low.

The compressor 100, shown in FIG. 2, also includes a feature forlubricating and cooling. This feature is provided for by liquidrefrigerant coupled to a nozzle 161 that is fixed to the left end ofhousing and extends into the shaft 12. The nozzle 161 is provided withlabyrinths 162 around which the refrigerant expands, providingliquid-vapor mixture to cool and lubricate the hearing 101. Therefrigerant also expands out of radial holes 163 and 164 formed in theshaft to spray cold refrigerant on the field coils 166. At the other endof shaft 12, hearing 102 is cooled and lubricated by refrigerantexpanding from radial holes 167 also formed in shaft 12. The refrigerantthat flows over the bearing 102 passes through a port 171 which iscoupled to a suitable tube, not shown, and fed into the intake 118. Therefrigerant that cools bearing 101 and the motor enter stage A through aport 172 formed in member 123. Port 172 could be placed in such aposition that gravity would cause any accumulated liquid to flow intoinlet 118.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, all matter contained in theabove description or shown in the accompanying drawings is intended tobe interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A refrigeration system comprising:

a compressor having a plurality of stages for compressing a refrigerantin each stage to a higher pressure;

a condenser for liquefying the refrigerant after it is compressed bysaid compressor;

an evaporator for vaporizing the liquid into a vapor to be againcompressed by said compressor;

means for sensing the refrigeration temperature of said system;

means, responsive to said means for sensing, for unloading the stagesone at a time as the refrigeration requiriments drop and for reloadingthe stages one at a time as the refrigeration requirements increase,

said compressor being a centrifugal type and each of said stagesoperating at a steady rotational speed,

said means for unloading including a by-pass duct for at least one stageand a valve operated by said means for sensing,

at least one of said stages including a vaneless toroidal housingthrough which the refrigerant passes to absorb energy;

a plurality of impeller blades extending into said housing and disposedto move with respect to said housmg;

a wheel, on which said impeller blades are mounted, said wheel beingdisposed coaxially with said toroidal housing;

a shaft for carrying said wheel in rotation,

a casing for enclosing said stages,

an electric motor disposed within said casing for rotating said wheel,

said shaft being hollow,

means for feeding liquid refrigerant within said rotating shaft, and

port means on said shaft for causing the liquid to leave said shaft andexpand within said casing to provide cooling for the components disposedwithin said casmg.

2. A refrigeration system comprising:

a compressor having a plurality of stages for compressing a refrigerantin each stage to a higher pressure;

a condenser for liquefying the refrigerant after it is compressed bysaid compressor;

an evaporator for vaporizing the liquid into a vapor to be againcompressed by said compressor;

means for sensing the refrigeration temperature of said system;

means, responsive to said means for sensing, for unloading the stagesone at a time as the refrigeration requirements drop and for reloadingthe stages one at a time as the refrigeration requirements increase,

at least one of said stages includinga vaneless toroidal housing throughwhich the refrigerant passes to absorb energy;

a plurality of impeller blades extending into said housing and disposedto move with respect to said housa wheel on which said impeller bladesare mounted and said wheel is disposed coaxially with said toroidalhousing; and

a shaft for carrying said wheel in rotation.

3. The system of claim 2 wherein:

a casing is provided for enclosing said stages,

an induction electric motor is disposed within said casing for rotatingsaid shaft,

said shaft is hollow,

means are provided for feeding liquid refrigerant within said rotatingshaft,

port means on said shaft for causing the liquid to leave said shaft andexpand within said casing to provide cooling for the components disposedwithin said casing.

4. A refrigeration system comprising:

a compressor having an inlet and a first outlet whereby said refrigerantnormally enters said inlet and exits from said outlet at a higherpressure;

a condenser;

an evaporator;

first means for sensing the refrigeration temperature of saidevaporator;

said compressor having at least another outlet between said inlet andsaid first outlet;

second means for connecting said other outlet with said inlet;

third means disposed in said second means so that said other outletcommunicates with said inlet in response to said first means wheneversaid refrigeration temperature tends to drop,

said compressor including a vaneless toroidal housing;

a plurality of impeller blades extending into said housing and disposedto move with respect to said housa Wheel on which said blades aremounted and which wheel is disposed coaxially with said toroidal housashaft for carrying said wheel in rotation,

a casing for enclosing said stages,

an electric motor disposed within said casing for rotating said wheel,

said shaft being hollow,

means for feeding liquid refrigerant within said rotating shaft, and

port means on said shaft for causing the liquid to leave said shaft andexpand within said casing to provide cooling for the components disposedwithin said casing.

5. The system of claim 4 wherein:

said second means includes a duct connecting said other outlet with saidinlet; and

said third means includes a valve.

References Cited UNITED STATES PATENTS 2,401,827 6/1946 Heitchoe 62 196XR 2,555,005 5/1951 Warneke 62196 XR 3,041,847 7/1962 Harter 62228 XR3,350,896 7/1967 Harnish 62228 XR MEYER PERLIN, Primary Examiner US. Cl.X.R.

